Difference Between Plum and PlumbPlum has the following meanings:-
1. The fruit from one of several trees which is smooth skinned and with a large seed or pit in the middle: ” I avoid eating plum fruit fearing that it may spoil my throat.”
2. A color that is dark reddish or purple in tone: “Her coat having a combination of plum and black colors suited her fair complexion.”

Plumb, on the other hand, has the following meanings:-
1. A weight on the end of a line, used to determine water depth: “Let us use a stone as a plumb to measure the depth of the water in the pond.”
2. A weight on the end of a line, used especially by masons and carpenters to establish a true vertical: “The masons make use of plumb to establish the straightness of the wall.”